Question: What's the first wrong statement in the proof below that $ \triangle CEF \cong \triangle CEB$ $ \; ?$ $ \overline{BC} $ is parallel to $ \overline{DF} $. This diagram is not drawn to scale. $A$ $B$ $C$ $D$ $E$ $F$ Givens $ \overline{AB} \cong \overline{EF}$ $, \ $ $ \angle BAC \cong \angle CEF$ $, \ $ $ \overline{AC} \cong \overline{CE}$ $, \ $ $ \overline{DE} \cong \overline{CE}$ $, \ $ $ \angle BDE \cong \angle ECF$ $, \ $ and $\ $ $ \overline{BD} \cong \overline{CF}$ Proof $ \triangle CEF \cong \triangle CAB$ because SAS $ \angle CEF \cong \angle CBE$ because alternate interior angles are equal $ \overline{CF} \cong \overline{BC}$ because corresponding parts of congruent triangles are congruent $ \triangle DEB \cong \triangle CEF$ because SAS $ \angle CFE \cong \angle DBE$ because corresponding parts of congruent triangles are congruent $ \triangle CEF \cong \triangle CEB$ because SSS
Solution: Try going through the proof yourself: write down the givens, and then see if they justify the next step for the reason given. Then do the same thing for the next step, and the next, until you run into something that you can't justify, or you finish the proof. $ \angle CBE \cong \angle CEF$ is the first wrong statement.